Bicycle frame with improved weld joint

ABSTRACT

A bicycle frame comprising a first tubular member having a first interface portion, and a second tubular member having a second interface portion engaged with the first interface portion to create a joint. The joint includes a peripheral channel having a depth that is greater than a wall thickness of the first tubular member, and a weld is positioned in the peripheral channel. To enhance the transition from the first main portion to the second main portion, the second tubular member can include a fillet surface between the second main portion and the second interface portion. The fillet surface is contoured to provide a smooth transition between the top tube and the head tube. An outer surface of the first interface portion can be offset from an outer surface of the first main portion to thereby create a shoulder.

BACKGROUND

The present invention relates to bicycle frames, and particularly toweld joints of tubular bicycle frames.

Bicycle frames are commonly manufactured from tubes that are coupledtogether into a desired configuration. When the tubes are metal (e.g.,steel, aluminum, titanium, etc.), they can be welded together to formthe bicycle frame. When manufacturing a welded bicycle frame, the endsof the tubes are pre-cut so that the tubes fit together to form pre-weldjoints between the tubes. For example, one tube can be mitered so thatit wraps snugly around the tube to which it will be welded. When tubesof similar size are coupled using a mitered joint, the geometry of thejoint varies dramatically around the tube interface, from essentially aT-joint at the top and bottom to essentially a tangent joint on thesides, with the mitered tube having a razor thin wall thickness at thetangent joint.

When welding tubes having mitered joints, a weld fillet is formed aroundthe joint. Due to the varying joint geometry of the above-describedmitered joint, creating a good, consistent weld is very difficult. Atthe location where the tubes are tangent, the weld bead commonlyprotrudes substantially above the surfaces of the tubes being welded. Ifa smooth joint is desired, one would need to grind or sand the weldbead.

SUMMARY

The present invention relates to an improved weld joint structurebetween two parts. This improved joint structure is designed to make theweld bead more flush with the outer surfaces of the parts being weldedto give the appearance of a smooth transition between the outer surfacesof the parts, and to reduce or eliminate post-weld finishing operations,such as grinding or sanding.

The invention provides a bicycle frame comprising a first tubular memberhaving a first main portion and a first interface portion (e.g., a firsttapered portion), a second tubular member having a second main portionand a second interface portion (e.g., a second tapered portion) engagedwith the first interface portion to create a joint. The joint includes aperipheral channel defined between the first interface portion and thesecond interface portion. The channel has a depth that is greater than awall thickness of the first tubular member, and a weld is positioned inthe peripheral channel. In one embodiment, a ratio of the channel depthto the wall thickness is at least 1.5:1, and is preferably at least 2:1.

To enhance the transition from the first main portion to the second mainportion, the second tubular member can include a fillet surface betweenthe second main portion and the second interface portion. The filletsurface is contoured to provide a smooth transition between the top tubeand the head tube.

In order to create a visual guide to the welder, an outer surface of thefirst interface portion can be offset from an outer surface of the firstmain portion to thereby create a shoulder. In one embodiment, a ratio ofa shoulder depth to the wall thickness is at least 1:10, preferably atleast 1:5, and more preferably at least 1:3.

In order to enhance the dry fit of the first and second tubular members,the first interface portion can be dimensioned to fit inside the secondinterface portion (e.g., a inner dimension of the first interfaceportion can be less than a corresponding inner dimension of the secondinterface portion. In a situation where one of the interface portionshas a thinner wall thickness than the other interface portion, it ispreferred that the thinner interface portion be positioned inside thethicker interface portion.

It is anticipated that some aspects of this invention are applicable tobicycle components other than frames. Other aspects of the inventionwill become apparent by consideration of the detailed description andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a bicycle including a welded frame havingfeatures of the present invention.

FIG. 2 is an enlarged partial side view of a portion of the frame priorto welding.

FIG. 3 is an exploded perspective view of the portion of the framedepicted in FIG. 2.

FIG. 4 is a section view of the portion of the frame depicted in FIG. 2.

FIG. 5 is an enlarged view of one of the joints shown in FIG. 2.

FIG. 6 is the section view of FIG. 4 after the tubes are weldedtogether.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways.

FIG. 1 illustrates a bicycle 10 that includes a front wheel 12, a rearwheel 14, a frame 16, and a steering assembly 18. The frame 16 includesa top tube 20, a head tube 22, a down tube 24, a seat tube 26, seatstays28, chainstays 30, and a bottom bracket 32. Pedals 34 are attached to acrankset 36 to allow a user to rotate the crankset 36 and to propel thebicycle 10, as is known in the art.

FIG. 2 is an enlarged side view of the head tube 22 and portions of thetop tube 20 and down tube 24 prior to those tubes being securedtogether. Each of the top tube 20 and down tube 24 includes a mainportion 40 having a generally smooth outer surface 42 that is generallyparallel to a longitudinal axis 44 of the tube. The illustrated mainportions 40 are generally circular or oval in cross section. However,the present invention is not limited to tubes having circular or ovalcross sections, but is applicable to tubes having a variety of crosssections.

The end of each of the top tube 20 and down tube 24 includes aninterface portion in the form of a tapered portion 50 that extends at anangle relative to the main portion 40 of each tube. The angle of thetapered portion 50 varies depending on the position around the perimeterof the tube. In this illustrated embodiment, the angle a of the taperedportion 50 of the top tube 20 relative to the longitudinal axis 44 ofthe top tube 20 varies from about 27 degrees to about 51 degrees. Theangle β of the tapered portion 50 of the down tube 24 relative to thelongitudinal axis 44 of the down tube 24 varies from about 8 degrees toabout 66 degrees.

With continued reference to FIG. 2, the head tube 22 comprises a mainportion 52 having an outer surface 54 that generally mimics acylindrical and/or slightly frustoconical configuration. The head tube22 further includes an upper fillet surface 60 that is designed toprovide a smooth transition from the outer surface 54 of the head tube22 to the outer surface 42 of the main portion 40 of the top tube 20.The head tube 22 also includes a lower fillet surface 62 that isdesigned to provide a smooth transition from the outer surface 54 of thehead tube 22 to the outer surface 42 of the main portion 40 of the downtube 24. More specifically, the upper and lower fillet surfaces 60, 62are designed to mimic a weld fillet that would appear if substantiallystraight tubes were welded together (e.g., using a mitered joint) andsanded to provide a smooth, radiused transition between the head tube 22and the top and down tubes 24, respectively, thus giving the appearanceof a molded frame 16.

The head tube 22 further includes an upper tapered portion 64 extendingat an angle from the upper fillet surface 60, and a lower taperedportion 66 extending at an angle from the lower fillet surface 62. Theupper and lower tapered portions 64, 66 are designed to fit with thetapered portions 50 of the top tube 20 and down tube 24, respectively,to form pre-weld joints. The angle of the upper and lower taperedportions 64, 66 varies around the perimeter of the upper and lowerfillet surfaces 60,62. In the illustrated embodiment, the angle of theupper tapered portion 64 is about 36 degrees to about 91 degreesrelative to the longitudinal axis 44 of the top tube 20. The angle ofthe lower tapered 66 portion varies from about 30 degrees to about 59degrees relative to the longitudinal axis 44 of the down tube 24.

Referring to FIG. 4, the end of the tapered portion 50 of the top tube20 fits inside the end of the upper tapered portion 64 of the head tube22. In other words, an outer surface 70 of the tapered portion 50 of thetop tube 20 engages an inner edge 72 or surface of the upper taperedportion 64. In this regard, it can be seen that an inner dimension 74 ofthe tapered portion 50 of the top tube 20 is smaller than acorresponding inner dimension 76 of the upper tapered portion 64.Similarly, the end of the tapered portion 50 of the down tube 24 fitswithin the end of the lower tapered portion 66 of the head tube 22. Thisconfiguration provides for a relatively secure dry fit between the tubesprior to the welding operation, which facilitates the proper alignmentand positioning of the tubes relative to each other. The above-describedarrangement could be reversed, with one or both of the upper and lowertapered portions 64, 66 fitting inside the corresponding tapered portion50 of the top tube 20 and down tube 24, respectively. However, it isconsidered desirable to have the thinner tube (i.e., the top tube anddown tube in the illustrated embodiment) positioned inside the thickertube (i.e., the head tube in the illustrated embodiment).

With further reference to FIGS. 2 and 4, the above-describedconfiguration of top tube 20, down tube 24, and head tube 22 results increation of a peripheral channel 80 around the joint between the toptube 20 and head tube 22 and the joint between the down tube 24 and headtube 22. These channels 80 are dimensioned such that the cross-sectionalarea of each channel (i.e., the triangular region defined by the taperedportions) does not vary substantially around the perimeter of the joint.The result is a substantially uniform cross-section weld joint that iseasier to weld. With skilled welders, it is believed that welding ofthese joints can result in a near finished products, with the weld beadsubstantially flush with the adjacent surfaces, thus requiring little orno grinding, filing, or sanding.

The illustrated peripheral channels 80 are substantially V-shaped, andan angle γ at the base of the channel varies between about 80 degreesand about 96 degrees. In the illustrated embodiment, the channels have adepth 82 that is greater than the wall thickness 84 of the tubes beingwelded. For example, the depth 82 (FIG. 5) of the channel between thetop tube 20 and head tube 22 is about 5 millimeters, and a wallthicknesses 84 of the top tube and head tube at the joint (i.e., theinterface portions) are about 2 mm and 2.5 mm, respectively. In thisconfiguration, the ratio between the channel depth and the tube wallthickness is about 2.5:1 for the top tube and about 2:1 for the headtube.

It should be understood that the channels do not need to have straightsidewalls, but instead could have curved sidewalls, such as when thetube ends are domed.

FIG. 5 illustrates an enlarged view of one of the V-shaped channels 80created by the above-described tapered portions 50, 64. This enlargedview shows that the illustrated tapered portions 50, 64 do not extenddirectly from the ends of the outer surfaces 42, 60 of the tubes.Rather, each tapered portion 50, 64 is offset such that there is ashoulder 86 between the outer surfaces 42, 60 and the tapered portions50, 64. The illustrated shoulder 86 is radiused, but could instead bestraight. The illustrated shoulder has a shoulder depth 88 of about 0.5mm, thus creating shoulder depth 88 to wall thickness ratio of about1:3. This offset between the tapered portions 50, 64 and the outersurfaces 42, 60 provides a guide for the welder, thus facilitating abetter weld. It should be understood that the shoulder could be sizeddifferently from the described embodiment, or the shoulder could beeliminated entirely without detracting from certain aspects of thepresent invention.

FIG. 6 illustrates weld beads 92 (in broken lines) after the joints arewelded. As illustrated, the weld beads 92 are substantially flush, ormight protrude slightly outward from the joint beyond the outer surfacesof the tubes. The weld 92 can then be finished (e.g., ground, filed,sanded, etc.), if necessary, until it is flush with the outer surfacesof the tubes. The result is a welded bicycle frame that, once painted,will look like a single-piece molded bicycle frame.

Various features and advantages of the invention are set forth in thefollowing claims.

1. A bicycle frame comprising: a first tubular member having a firstmain portion and a first interface portion; a second tubular memberhaving a second main portion and a second interface portion engaged withthe first interface portion to create a joint, wherein the jointincludes a peripheral channel defined between the first interfaceportion and the second interface portion, the channel having a channeldepth that is greater than a wall thickness of the first tubular member;and a weld positioned in the peripheral channel.
 2. A bicycle frame asclaimed in claim 1, wherein the first interface portion comprises afirst tapered portion.
 3. A bicycle frame as claimed in claim 2, whereinthe second interface portion comprises a second tapered portion engagedwith the first tapered portion.
 4. A bicycle frame as claimed in claim1, wherein a ratio of the channel depth to the wall thickness is atleast 1.5:1.
 5. A bicycle frame as claimed in claim 1, wherein a ratioof the channel depth to the wall thickness is at least 2:1.
 6. A bicycleframe as claimed in claim 1, wherein the peripheral channel issubstantially V-shaped.
 7. A bicycle frame as claimed in claim 1,wherein an outer surface of the first interface portion is offset froman outer surface of the first main portion to thereby create a shoulder.8. A bicycle frame as claimed in claim 7, wherein the shoulder has ashoulder depth, and wherein a ratio of the shoulder depth to the wallthickness is at least 1:10.
 9. A bicycle frame as claimed in claim 1,wherein the first interface portion fits inside the second interfaceportion.
 10. A bicycle frame as claimed in claim 1, wherein the wallthickness of the first interface portion is thinner than a wallthickness of the second interface portion.
 11. A bicycle frame asclaimed in claim 1, wherein the first interface portion includes aninner dimension that is smaller than a corresponding inner dimension ofthe second interface portion.
 12. A bicycle frame comprising: a firsttubular member having a first main portion and a first interfaceportion; a second tubular member having a second main portion, a secondinterface portion engaged with the first interface portion to create ajoint, and a fillet surface between the second main portion and thesecond interface portion, wherein the joint includes a peripheralchannel defined between the first interface portion and the secondinterface portion; and a weld positioned in the peripheral channel. 13.A bicycle frame as claimed in claim 12, wherein the first interfaceportion comprises a first tapered portion, and the second interfaceportion comprises a second tapered portion engaged with the firsttapered portion.
 14. A bicycle frame as claimed in claim 12, wherein theperipheral channel is substantially V-shaped.
 15. A bicycle frame asclaimed in claim 12, wherein an outer surface of the first interfaceportion is offset from an outer surface of the first main portion tothereby create a shoulder.
 16. A bicycle frame as claimed in claim 12,wherein the first interface portion fits inside the second interfaceportion.
 17. A bicycle frame as claimed in claim 16, wherein the wallthickness of the first interface portion is thinner than a wallthickness of the second interface portion.
 18. A bicycle framecomprising: a first tubular member having a first main portion and afirst interface portion having a wall thickness; a second tubular memberhaving a second main portion and a second interface portion engaged withthe first interface portion to create a joint, and a fillet surfacebetween the second main portion and the second interface portion,wherein the joint includes a peripheral channel defined between thefirst interface portion and the second interface portion, the channelhaving a depth, wherein a ratio of the depth to the wall thickness is atleast 1.5:1; and a weld positioned in the peripheral channel.
 19. Abicycle frame as claimed in claim 1, wherein an interior surface of thefirst tubular member tapers radially inward adjacent the first interfaceportion.
 20. A bicycle frame as claimed in claim 12, wherein an interiorsurface of the first tubular member tapers radially inward adjacent thefirst interface portion.